Self-Aligned Double Spacer Patterning Process

ABSTRACT

Embodiments of the present disclosure are a method of forming a semiconductor device and methods of patterning a semiconductor device. An embodiment is a method of forming a semiconductor device, the method including forming a first hard mask layer over a semiconductor device layer, forming a set of mandrels over the first hard mask layer, and forming a first spacer layer over the set of mandrels and the first hard mask layer. The method further includes forming a second spacer layer over the first spacer layer, patterning the first spacer layer and the second spacer layer to form a mask pattern, and patterning the first hard mask layer using the mask pattern as a mask.

This application is a continuation of U.S. patent application Ser. No.14/820,183, filed Aug. 6, 2015, entitled “Self-Aligned Double SpacerPatterning Process,” which is a continuation of Ser. No. 14/096,963,filed Dec. 4, 2013 (now U.S. Pat. No. 9,123,776, issued Sep. 1, 2015,entitled “Self-Aligned Double Spacer Patterning Process,” which patentapplications are incorporated herein by reference in their entirety.

BACKGROUND

With the increasing down-scaling of semiconductor devices, variousprocessing techniques, such as, photolithography are adapted to allowfor the manufacture of devices with increasingly smaller dimensions.However, as semiconductor processes require smaller process windows, themanufacture of these devices have approached and even surpassed thetheoretical limits of photolithography equipment. As semiconductordevices continue to shrink, the spacing desired between elements (i.e.,the pitch) of a device is less than the pitch that can be manufacturedusing traditional optical masks and photolithography equipment.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present embodiments, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawings, in which:

FIGS. 1A, 1B, 2A, 2B, 3A, 3B, 4A, 4B, 5A, 5B, 6A, 6B, 7A, 7B, 8A, 8B,9A, 9B, 10A, 10B, 11, and 12 are top-views and cross-sectional views ofintermediate stages in the patterning of a semiconductor device inaccordance with an embodiment.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

Reference will now be made in detail to embodiments illustrated in theaccompanying drawings. Wherever possible, the same reference numbers areused in the drawings and the description to refer to the same or likeparts. In the drawings, the shape and thickness may be exaggerated forclarity and convenience. This description will be directed in particularto elements forming part of, or cooperating more directly with, methodsand apparatus in accordance with the present disclosure. It is to beunderstood that elements not specifically shown or described may takevarious forms well known to those skilled in the art. Many alternativesand modifications will be apparent to those skilled in the art, onceinformed by the present disclosure.

Reference throughout this specification to “one embodiment” or “anembodiment” means that a particular feature, structure, orcharacteristic described in connection with the embodiment is includedin at least one embodiment. Thus, the appearances of the phrases “in oneembodiment” or “in an embodiment” in various places throughout thisspecification are not necessarily all referring to the same embodiment.Furthermore, the particular features, structures, or characteristics maybe combined in any suitable manner in one or more embodiments. It shouldbe appreciated that the following figures are not drawn to scale;rather, these figures are merely intended for illustration.

Embodiments will be described with respect to a method for patterning asemiconductor device layer by transferring multiple patterns to a hardmask layer over the semiconductor device layer. At least one of thepatterns includes a first spacer conformally deposited over mandrels anda second spacer layer deposited over the first spacer layer.

FIGS. 1A through 12 are top views and cross-sectional views ofintermediate stages in the patterning of a semiconductor device 100 inaccordance with an embodiment. FIGS. 1A and 1B illustrate a top view anda cross-sectional view, respectively, of a semiconductor device 100 atan intermediate stage of processing. FIG. 1B is a cross-sectional viewalong the line A-A in FIG. 1A. FIGS. 2B through 10B are alsocross-sectional views along the same line A-A in each of the respectivetop view (FIGS. 2A through 10A), although the line A-A is not shown onthese subsequent Figures.

Referring to FIGS. 1A and 1B, the semiconductor device 100 includes asemiconductor device layer 20, an anti-reflective coating (ARC) 22, hardmask layers 24 and 26, and a tri-layer photoresist 34 over the hard masklayers 24 and 26. The semiconductor device layer 20 is a layer thatrequires patterning. In some embodiments, the semiconductor device layer20 is a metallic layer to be used for metal lines and is made of copper,aluminum, the like, or a combination thereof. In other embodiments, thesemiconductor device layer 20 is a dielectric layer, such as a low-kdielectric layer, a polymer layer, or the like. In yet otherembodiments, the semiconductor device layer 20 is a substrate and ismade of a semiconductor material such as silicon, germanium, diamond, orthe like. Alternatively, compound materials such as silicon germanium,silicon carbide, gallium arsenic, indium arsenide, indium phosphide,silicon germanium carbide, gallium arsenic phosphide, gallium indiumphosphide, combinations of these, and the like, may also be used. In theembodiments wherein the semiconductor device layer 20 is not asubstrate, a substrate (not shown) may be below the semiconductor devicelayer 20. The substrate (not shown) may be formed of similar materialsas described above, and the description will not be repeated herein.

The substrate (not shown) or in the embodiment wherein the semiconductordevice layer 20 is a substrate may include active and passive devices(not shown). As one of ordinary skill in the art will recognize, a widevariety of devices such as transistors, capacitors, resistors,combinations of these, and the like may be used to generate thestructural and functional requirements of the design for thesemiconductor device 100. The active and passive devices may be formedusing any suitable methods.

The ARC 22 may be formed over the semiconductor device layer 20. The ARC22 prevents radiation in subsequent photolithographic processes fromreflecting off layers below and interfering with the exposure process.Such interference can increase the critical dimension of thephotolithography process. Sometimes the ARC 22 is referred to as ananti-reflective layer (ARL) 22. In some embodiments, the ARC 22 is anitrogen-free ARC (NFARC) 22 and is made of a silicon-rich oxide (SRO),silicon oxycarbide, the like, or a combination thereof. In someembodiments, the ARC 22 is formed by chemical vapor deposition (CVD),plasma enhanced CVD (PECVD), the like, or a combination thereof.

The hard mask layers 24 and 26 are formed over the ARC 22. In anembodiment, the hard mask layer 24 is a metal hard mask layer and thehard mask layer 26 is a dielectric hard mask layer. In subsequentprocessing steps, a pattern is transferred onto the hard mask layer 24using various photolithography and etching techniques. The hard masklayer 24 may then be used as a patterning mask for etching theunderlying ARC 22 and the semiconductor device layer 20 (see FIG. 11).The hard mask layer 24 may be a masking material such as titaniumnitride, tetraethyl orthosilicate (TEOS), silicon nitride, the like, ora combination thereof. The hard mask layer 24 may be formed using aprocess such as CVD, physical vapor deposition (PVD), atomic layerdeposition (ALD), the like, or a combination thereof. In an embodiment,the hard mask layer 24 is formed to have a thickness from about 300Angstroms to about 1000 Angstroms.

The hard mask layer 26 is formed over the hard mask layer 24. The hardmask layer 26 may be used to form mandrels 26′ (see FIG. 3B) and will bereferred to as a mandrel layer 26 hereinafter. The mandrel layer 26 maybe a masking material such as silicon nitride, an oxide, silicon,amorphous silicon, the like, or a combination thereof or any othermaterial that may be patterned and selectively removed. The mandrellayer 26 may be formed using a process such as CVD, ALD, the like, or acombination thereof. In an embodiment, the mandrel layer 26 is formed tohave a thickness from about 500 Angstroms to about 1200 Angstroms.

The tri-layer photoresist 34 is formed over the mandrel layer 26. Thetri-layer photoresist 34 includes a top photoresist layer 32, a middlelayer 30, and a bottom layer 28. As the limits of photolithographyprocesses are reached by advanced semiconductor manufacturing processes,the need for thinner top photoresist layers has arisen to achievesmaller process windows. However, thin top photoresist layers may not besufficiently robust to support the etching of target layers (e.g., themandrel layer 26). The tri-layer photoresist provides a relatively thintop photoresist layer 32. The middle layer 30 may includeanti-reflective materials (e.g., a backside anti-reflective coating(BARC) layer) to aid the exposure and focus of the top photoresist layer32's processing. By having the middle layer 30, the thin top photoresistlayer 32 is only used to pattern the middle layer 30. The bottom layer28 may include a hard mask material such as a carbon-containing materialthat is easily removed by O₂ or a N₂/H₂ plasma. The middle layer 30 isused to pattern the bottom layer 28. In some embodiments, the middlelayer 30 has a high etch selectivity to the bottom layer 28, and, insome embodiments, the bottom layer 28 is more than ten times thickerthan the middle layer 30. Thus, the tri-layer photoresist 34 allows forthe robust patterning of underlying layers (e.g., the mandrel layer 26)while still providing a relatively thin top photoresist layer 32.

The top photoresist layer 32 may be patterned using any suitablephotolithography technique. For example, a photomask (not shown) may bedisposed over the top photoresist layer 32, which may then be exposed toa radiation beam including an ultraviolet (UV) or an excimer laser suchas a 248 nm beam from a Krypton Fluoride (KrF) excimer laser, or a 193nm beam from an Argon Fluoride (ArF) excimer laser. Exposure of the topphotoresist layer 32 may be performed using an immersion lithographysystem to increase resolution and decrease the minimum achievable pitch.A bake or cure operation may be performed to harden the top photoresistlayer 32, and a developer may be used to remove either the exposed orunexposed portions of the top photoresist layer 32 depending on whethera positive or negative resist is used. Thus, a pattern such as thepattern illustrated in FIGS. 1A and 1B is formed in the top photoresistlayer 32 including the two openings 36 in the top photoresist layer 32each having a width W₁ and another opening 38 capable of having variouswidths depending on the design of the semiconductor device 100. The twoopenings 36 are separated by a width W₂. The widths W₁, W₂, andsubsequent widths are described in terms of the desired spacing and/orwidth of a pattern to be applied to the semiconductor device layer 20(see FIGS. 10A and 10B) which will represented by X. In an embodiment,the width W₁ is about 3X and the width W₂ is about 3X. In an exemplaryembodiment, the desired spacing and width value of X is 16 nm. In thisexample, the pitch of the resulting pattern would be 32 nm (see FIGS.10A and 10B), the width W₁ (3X) would be about 48 nm, and the width W₂(3X) would be about 48 nm.

FIGS. 1A and 1B illustrate two openings 36 and another opening 38 in thetop photoresist layer 32, although there may be more or less openingsdepending on the number of mandrels 26′ and trenches 60 and 62 that aredesired (see FIG. 11). In addition, although the width and spacing ofthe trenches 60 in FIGS. 11 are equal, this disclosure contemplatesother embodiments wherein the width and spacing of the trenches 60 arenot equal.

FIGS. 2A and 2B illustrate the resulting structure after the topphotoresist layer 32 has been trimmed. In an embodiment, the trimmingprocess is an anisotropic plasma etch process with process gasesincluding O₂, CO2, N2/H2, H2, the like, a combination thereof, or anyother gases suitable for trimming photoresist. In an embodiment, thephotoresist trimming process is performed at a temperature from about20° C. to about 80° C., at a pressure from about 20 milliTorr to about150 milliTorr, for a duration of about 30 seconds to about 2 minutes.The variables in the photoresist trimming process may be varied based onthe desired final photoresist profile. After the photoresist trimprocess, the two openings 36 of the top photoresist layer 32 each havewidths W₅. The two openings 36 are separated by a width W₆. In someembodiment, the width W₅ is larger than the width W₁ and the width W₆ issmaller than the width W₂. In an embodiment, width W₅ is about 5X andthe width W₆ is about 1X. In the embodiment where X is about 16 nm, W₅is about 80 nm and W₆ is about 16 nm. In some embodiments, the opening38 also has larger width than before the photoresist trimming process.

FIGS. 3A and 3B illustrate the resulting structure after the mandrellayer 26 has been patterned forming openings and mandrels 26′. Afterdeveloping and patterning the top photoresist layer 32, the pattern istransferred to the middle and bottom layers 30 and 28, respectively. Thepattern may be transferred, for example, by one or more selectiveetching processes. After the selective etching processes, the topphotoresist layer 32 and the middle layer 30 may be removed by, forexample, another trimming process such as an anisotropic plasma etchprocess. In some embodiments, portions of the bottom layer 28 are alsoremoved during the trimming process to achieve a more stable aspectratio for subsequent etching steps. In an embodiment, the mandrel layer26 is etched using the bottom layer 28 as a patterning mask forming themandrels 26′. In this embodiment, the remaining portions of the bottomlayer 28 are removed by, for example, an in-situ O₂ or H₂ plasmaprocess. In another embodiment, the trimming process is omitted, and themandrel layer 26 is patterned using all three of three layers (32, 30,and 28) of the tri-layer photoresist 34 forming the mandrels 26′. Insome embodiments, the mandrel layer 26 is patterned by a dry etchprocess with etch process gases including Br, O₂, N₂, H₂, CxFy, thelike, or a combination thereof. In an embodiment, the mandrel patterningprocess is performed at a temperature from about 20° C. to about 80° C.,at a pressure from about 20 milliTorr to about 150 milliTorr, for aduration of about 30 seconds to about 2 minutes. As illustrated in FIGS.3A and 3B, the mandrel 26′ patterned by the portion of the topphotoresist layer 32 between the openings 36 of the top photoresistlayer 32 (see FIGS. 2A and 2B) has the width W₆ and is spaced apart fromadjacent mandrels 26′ by the widths W₅.

After the mandrels 26′ are formed, a spacer layer 40 is formed over themandrels 26′ and the hard mask layer 24 as illustrated in FIGS. 4A and4B. In an embodiment, the spacer layer 40 is conformally deposited overthe mandrels 26′ and the hard mask layer 24 such that the thickness T₁of the spacer layer on the top surface of the hard mask layer 24 and thesidewalls of the mandrels 26′ is substantially a same thickness. In someembodiments, the spacer layer 40 is a metal-containing spacer layer 40and is made of, titanium nitride, titanium oxide, the like, or acombination thereof. In an embodiment, the spacer layer 40 is an oxide.The material of the spacer layer 40 is selected to have a high etchselectivity to the hard mask layer 24, the mandrels 26′, and thesubsequently formed spacer layer 42 (see FIGS. 5A and 5B) so thatsubsequent etching steps may be performed on the spacer layer 40 withoutattacking the hard mask layer 24, the mandrels 26′, and the spacer layer42. The spacer layer 40 may be deposited through a process such as ALD,CVD, PVD, the like, or a combination thereof, although any acceptableprocess may be utilized to form the spacer layer 40 to a thickness fromabout 50 Angstroms to about 250 Angstroms. Further, the thickness of thespacer layer 40 may be selected to determine the thickness of featureseventually formed in the semiconductor device layer 20.

After the spacer layer 40 is formed, a spacer layer 42 is formed overspacer layer 40 as illustrated in FIGS. 5A and 5B. In an embodiment, thespacer layer 42 is conformally deposited over spacer layer 40 such thatthe thickness T₂ of the spacer layer on the top surface of the spacerlayer 40 and the sidewalls of spacer layer 40 is substantially a samethickness. In an embodiment, the adjacent sidewalls of the spacer layer42 are separated by a distance D₁. The distance D₁ may be about 1X. Thedistance D₁ may be adjusted by varying the widths of the openingsbetween the mandrels 26′ and the thicknesses T₁ and T₂ of the spacerlayers 40 and 42, respectively. In some embodiments, the spacer layer 42is a metal-containing spacer layer 42 and is made of, titanium nitride,titanium oxide, the like, or a combination thereof. In an embodiment,the spacer layer 42 is a silicon nitride, an oxide, the like, or acombination thereof. The material of the spacer layer 42 is selected tohave a high etch selectivity to the spacer layer 40, the mandrels 26′,and the hard mask layer 24 so that subsequent etching steps may beperformed on the spacer layer 42 without attacking the spacer layer 40,the mandrels 26′, and the hard mask layer 24. In some embodiments, thespacer layer 42 and the spacer layer have a different materialcomposition so that the spacer layers may have a high etch selectivity.The spacer layer 42 may be deposited through a process such as ALD, CVD,PVD, the like, or a combination thereof, although any acceptable processmay be utilized to form the spacer layer 42 to a thickness from about 50Angstroms to about 250 Angstroms. In an embodiment, the thickness T₁ ofthe spacer layer 40 and the thickness T₂ of the spacer layer 42 are asubstantially same thickness. Further, the thickness of the spacer layer42 may be selected to determine the thickness of features eventuallyformed in the semiconductor device layer 20. In some embodiments, thethicknesses T₁ and T₂ are about 1X.

After the spacer layer 42 is formed over the spacer layer 40, the spacerlayer 42 may be etched to expose top surfaces of the spacer layer 40 andform spacers 42′ as illustrated in FIGS. 6A and 6B. The top portions ofthe spacer layer 42 may be anisotropically etched to expose theunderlying top surfaces of the spacer layer 40 to form the spacers 42′.The spacers 42′ are formed along the sidewalls of the spacer layer 40 inthe openings of the mandrel layer 26. In an embodiment, the etchant usedto etch the top portions of the spacer layer 42 is Br, Cl₂, O₂, N₂, H₂,CxFy, the like, a combination thereof, or any suitable etchant that canremove the top surfaces of the spacer layer 42.

FIGS. 7A and 7B illustrate the etching of the spacer layer 40. Thespacer layer 40 may be etched to expose top surfaces of the hard masklayer 24 and the mandrels 26′ to form spacers 40′. In an embodiment,each of the spacers 40′ adjoins at least two sides of a spacer 42′. Thetop portions of the spacer layer 40 may be anisotropically etched toexpose the underlying top surfaces of the hard mask layer 24 and themandrels 26′. The spacers 40′ are formed along the sidewalls of themandrels 26′ in the openings of the mandrel layer 26. In an embodiment,the etchant used to etch the top portions of the spacer layer 40 is Br,Cl₂, O₂, N₂, H₂, CxFy, the like, a combination thereof, or any suitableetchant that can remove the top surfaces of the spacer layer 40. In anembodiment, a bottom surface of each of the spacers 42′ adjoins a topsurface of a spacer 40′. Each of the spacers 40′ have a widthcorresponding to thickness T₁ and the spacers 42′ have a widthcorresponding to thickness T₂. The spacers 40′ and spacers 42′ form aset of combined spacers 46 with each combined spacer including onespacer 40′ and one spacer 42′.

After the spacers 40′ are formed, a tri-layer photoresist 56 is formedover the spacers 42′, the spacers 40′, and the mandrels 26′ asillustrated in FIGS. 8A and 8B. The tri-layer photoresist 56 may besubstantially similar to tri-layer photoresist 34 and includes arelatively thin top photoresist layer 54, a middle layer 52 (e.g., aBARC), and a bottom layer 50 (e.g., a hard mask material).

The top photoresist layer 54 may be patterned, for example, by using animmersion photolithography system including a radiation beam which maybe a 248 nm beam from a KrF excimer laser or a 193 nm beam from an ArFexcimer laser to expose portions of top photoresist layer 54 and developthe exposed/unexposed portions depending on whether a positive/negativephotoresist is used. Thus, a pattern such as the pattern illustrated inFIGS. 8A and 8B is formed in the top photoresist layer 54 including theopening in the top photoresist layer 54 over the spacers 42′, thespacers 40′, and the mandrels 26′ formed in the openings of the mandrellayer 26 corresponding to the openings 36 (see FIGS. 2A and 2B). Thispattern includes a portion of the top photoresist layer 54 coveringportions of the spacers 42′, portions of the spacers 40′, and portionsof the mandrels 26′ formed in the opening of the mandrel layer 26corresponding to the opening 38 (see FIGS. 2A and 2B). The pattern ofthe top photoresist layer 54 will be used to mask the portions of thespacers 40′ formed in the opening of the mandrel layer 26 correspondingto the opening 38 (see FIGS. 2A and 2B) such that the portions of thespacers 40′ formed in the openings of the mandrel layer 26 correspondingto the openings 36 (see FIGS. 2A and 2B) may be removed by a subsequentetching process. The pattern shown in FIGS. 8A and 8B is forillustrative purposes only and different patterns may be formeddepending on the design of semiconductor device 100.

FIGS. 9A and 9B illustrate the removal of the portions of the spacers40′ exposed in the opening of the top photoresist layer 54 (see FIGS. 8Aand 8B) forming the remaining portions of the spacers 40″ in theopening. The middle layer 52 and the bottom layer 50 of the tri-layerphotoresist 56 are patterned by the top photoresist layer 54 such thattop surfaces of the spacers 40′ are exposed. In an embodiment, theexposed spacers 40′ are patterned by a dry etch process with etchprocess gases including Br, Cl₂, O₂, N₂, H₂, CxFy, the like, acombination thereof, or any other suitable etchant that can remove theexposed portions of the spacers 40′ without damaging the spacers 42′ andthe mandrels 26′. The portions of the spacers 40′ are removed frombetween an adjacent mandrel 26′ and spacer 42′ and between adjacentspacers 42′. In some embodiments, each of the remaining portions of thespacers 40″ has a top surface that adjoins a bottom surface of a spacer42′. In an embodiment, each of the remaining portions of the spacers 40″adjoins only one side of a spacer 42′.

As illustrated in FIG. 9B, the pattern formed by the spacers 42′, theremaining portions of the spacers 40″, and the mandrels 26′ have widthsdetermined by the thickness T₂ of the spacer layer 42 and the width W₆of the mandrel 26′. This pattern has spacing determined by the thicknessT₁ of the spacer layer 40 and the distance D₁ between adjacent sidewallsof the spacer layer 42. Thus, if each the thicknesses T₁ and T₂, thewidth W₆, and the distances D₁ are about 1X, the pitch of the patternillustrated in FIG. 9B is 2X. In the exemplary embodiment where X isabout 16 nm, the pitch would be 32 nm.

As illustrated in FIGS. 10A and 10B, the pattern in FIGS. 9A and 9B maybe used to pattern the hard mask layer 24 to form a patterned hard masklayer 24′. In an embodiment, the hard mask layer 24 is patterned usingan etch process including etchant gases comprising Cl₂, Br, O₂, N₂, H₂,CxFy, the like, or a combination thereof.

FIG. 11 illustrates patterning the ARC 22 and the semiconductor devicelayer 20 using the patterned hard mask layer 24′ as a mask. The ARC 22may be patterned using the patterned hard mask layer 24′ as a mask. TheARC 22 may be patterned by an etch process including etchants such asC₄F₈, N₂, O₂, Ar, CxFy, the like, or a combination thereof. Thepatterned hard mask layer 24′ may be used to transfer the illustratedpattern to the semiconductor device layer 20, for example, through anetching process to form a patterned semiconductor device layer 20′. Inan embodiment, an upper portion of the he patterned semiconductor devicelayer 20′ has a plurality of trenches 60 and a trench 62 formed therein.The patterned hard mask layer 24′ and the ARC layer 22 may then beremoved as shown in FIG. 11. The plurality of trenches 60 may be filledwith a conductive material to form a plurality of conductive lines 64(see FIG. 12).

FIG. 12 illustrates forming a conductive material 64 over the patternedsemiconductor device layer 20′, filling the plurality of trenches 60.The conductive material 64 may include a barrier layer, a seed layer, aliner, or multiple layers or combinations thereof, for example, notshown. A fill material such as copper, a copper alloy, aluminum, analuminum alloy, the like, or a combination thereof may be formed overthe layers/liner using an electro-chemical plating (ECP) method and/orother deposition method. A chemical-mechanical polish (CMP) processand/or etch process may be used to remove excess conductive material 64from over the top surface of the patterned semiconductor device layer20′, as shown in FIG. 12, forming a plurality of conductive lines 64 inthe patterned semiconductor device layer 20′. The conductive lines 64have substantially the same pitch and spacing as the patterned hard masklayer 24′ shown in FIGS. 10A and 10B. In some embodiments, the trench 62is also filled with a conductive material to form a conductive feature(not shown).

The materials for the various layers may be selected to ensuresufficient etch selectivity between the layers. In an exemplaryembodiment, the hard mask layer 24 is titanium nitride, the mandrellayer 26 is TEOS, the spacer layer 40 is an oxide, and the spacer layer42 is silicon nitride. In another exemplary embodiment, the hard masklayer 24 is TEOS, the mandrel layer 26 is silicon, the spacer layer 40is titanium oxide, and the spacer layer 42 is silicon nitride. Inanother exemplary embodiment, the hard mask layer 24 is TEOS, themandrel layer 26 is silicon nitride, the spacer layer 40 is titaniumnitride, and the spacer layer 42 is silicon nitride. In anotherexemplary embodiment, the hard mask layer 24 is TEOS, the mandrel layer26 is silicon nitride, the spacer layer 40 is titanium oxide, and thespacer layer 42 is silicon nitride. In another exemplary embodiment, thehard mask layer 24 is silicon nitride, the mandrel layer 26 is an oxide,the spacer layer 40 is titanium oxide, and the spacer layer 42 is anoxide. These embodiments are only examples of possible combinations ofthe materials that may be used and the present disclosure is notintended to be limited to these particular embodiments.

By forming two spacer layers 40 and 42 with substantially the samethicknesses, quadruple patterning is achieved to reduce the pitch, whichallows the use of more proven lithography technology. For example, thecurrent process can use 96 nm pitch lithography and two 16 nm thickspacer layers to achieve a 32 nm pitch interconnect. Thus, the currentprocess can utilize 193 nm immersion lithography to achieve 32 nm pitchwhile also having a lower cost and higher throughput than the newerlithography methods such as extreme ultraviolet (EUV) lithography or thelike.

An embodiment is a method of forming a semiconductor device, the methodincluding forming a first hard mask layer over a semiconductor devicelayer, forming a set of mandrels over the first hard mask layer, andforming a first spacer layer over the set of mandrels and the first hardmask layer. The method further includes forming a second spacer layerover the first spacer layer, patterning the first spacer layer and thesecond spacer layer to form a mask pattern, and patterning the firsthard mask layer using the mask pattern as a mask.

Another embodiment is a method of patterning a semiconductor device, themethod including forming a first hard mask layer over a semiconductordevice layer, forming at least one mandrel over the first hard masklayer, conformally depositing a first spacer layer to have a uniformthickness over the at least one mandrel and the first hard mask layer,and conformally depositing a second spacer layer to have a uniformthickness over the first spacer layer. The method further includespatterning the first spacer layer and the second spacer layer to form afirst set of spacers on sidewalls of the at least one mandrel, each ofthe first set of spacers comprising a portion of the first spacer layerand a portion of the second spacer layer, each of the first set ofspacers having a first width, patterning the first set of spacers toform a second set of spacers over the first hard mask layer, each of thesecond set of spacers having a second width, the second width being lessthan the first width, and patterning the first hard mask layer and thesemiconductor device layer using the second set of spacers as a mask.

A further embodiment is a method of patterning a semiconductor device,the method including forming a second hard mask layer over a first hardmask layer and a semiconductor device layer, patterning the second hardmask layer to form a plurality of second hard mask portions, conformallyforming a first spacer layer over the plurality of second hard maskportions and the first hard mask layer, and conformally forming a secondspacer layer over the first spacer layer. The method further includesremoving top surfaces of the second spacer layer to expose top surfacesof the first spacer layer, removing the exposed top surfaces of thefirst spacer layer to expose top surfaces of the first hard mask layerand to form a mask pattern, and patterning the first hard mask layer andthe semiconductor device layer using the mask pattern as a mask.

Although the present embodiments and their advantages have beendescribed in detail, it should be understood that various changes,substitutions, and alterations can be made herein without departing fromthe spirit and scope of the disclosure as defined by the appendedclaims. Moreover, the scope of the present application is not intendedto be limited to the particular embodiments of the process, machine,manufacture, composition of matter, means, methods, and steps describedin the specification. As one of ordinary skill in the art will readilyappreciate from the disclosure, processes, machines, manufacture,compositions of matter, means, methods, or steps, presently existing orlater to be developed, that perform substantially the same function orachieve substantially the same result as the corresponding embodimentsdescribed herein may be utilized according to the present disclosure.Accordingly, the appended claims are intended to include within theirscope such processes, machines, manufacture, compositions of matter,means, methods, or steps.

What is claimed is:
 1. A method of forming a semiconductor structure,the method comprising: forming a mandrel layer over a semiconductorsubstrate; forming and patterning a photoresist over the mandrel layerto have first widths; trimming the patterned photoresist to have secondwidths; patterning the mandrel layer to form a first set of mandrelsusing the patterned and trimmed photoresist as a mask; forming a firstspacer layer over the first set of mandrels and the semiconductorsubstrate, the first spacer layer having second widths on at leastsidewalls of the first set of mandrels; forming a second spacer layerover the first spacer layer, the second spacer layer having secondwidths on at least sidewalls of the first spacer layer; patterning thefirst spacer layer and the second spacer layer; patterning thesemiconductor substrate to form trenches using the pattern of thepatterned first spacer layer and second spacer layer; and forming amaterial in the trenches of the semiconductor substrate.
 2. The methodof claim 1, wherein the material has a different material compositionthan the semiconductor substrate.
 3. The method of claim 1, wherein theforming the first spacer layer over the first set of mandrels and thesemiconductor substrate comprises: conformally depositing the firstspacer layer to have a thickness of the second width over the first setof mandrels and the semiconductor substrate.
 4. The method of claim 3,wherein the forming the second spacer layer over the first spacer layercomprises: conformally depositing the second spacer layer to have athickness of the second width over the first spacer layer.
 5. The methodof claim 1, wherein the second width is about one-third of the firstwidth.
 6. The method of claim 1, wherein at least one of the firstspacer layer and the second spacer layer is a metal-containing spacerlayer.
 7. The method of claim 1, wherein the patterning the first spacerlayer and the second spacer layer comprises: removing portions of thesecond spacer layer to expose the first spacer layer; removing firstportions of the exposed first spacer layer; and removing second portionsof the exposed first spacer layer between the first set of mandrels andremaining portions of the second spacer layer.
 8. The method of claim 7,wherein the removing first portions of the exposed first spacer layerforms a first set of spacers having a third width on sidewalls of thefirst set of mandrels, the third width being greater than the secondwidth.
 9. The method of claim 8, wherein the removing second portions ofthe exposed first spacer layer forms a second set of spacers of thesecond width.
 10. The method of claim 9, wherein at least two of thesecond set of spacers includes remaining portions of the first spacerlayer and the second spacer layer.
 11. The method of claim 9, wherein atleast one of the second set of spacers includes remaining one mandrel ofthe first set of mandrels.
 12. A method comprising: forming at least onemandrel over a first mask layer; depositing a first spacer layer overthe at least one mandrel and the first mask layer; depositing a secondspacer layer over the first spacer layer; etching the first spacer layerand the second spacer layer to form a first set of spacers on sidewallsof the at least one mandrel, each of the first set of spacers comprisinga portion of the first spacer layer and a portion of the second spacerlayer, each of the first set of spacers having a first width; etchingthe first set of spacers to form a second set of spacers over the firstmask layer, each of the second set of spacers having a second width, thesecond width being less than the first width; and etching the first masklayer using the second set of spacers as a mask.
 13. The method of claim12, wherein the forming at least one mandrel over the first mask layercomprises: forming a mandrel layer over the first mask layer; formingand patterning a photoresist over the mandrel layer to have thirdwidths; trimming the patterned photoresist to have the second widths;and patterning the mandrel layer to form the at least one mandrel usingthe patterned and trimmed photoresist as a mask.
 14. The method of claim12, wherein the second width is about one-half of the first width. 15.The method of claim 12, wherein each of the second set of spacers areseparated from adjacent spacers of the second set of spacers by a firstspacing, the first spacing being equal to the second width.
 16. Themethod of claim 12, wherein at least a portion of each of the second setof spacers comprises titanium.
 17. The method of claim 12, wherein theportion of the second spacer layer is on the portion of the first spacerlayer in each of the first set of spacers.
 18. A method comprising:forming a first mask layer over a semiconductor device layer; forming asecond mask layer over the first mask layer; forming and patterning athird mask layer over the second mask layer to form a plurality of thirdmask portions; patterning the second mask layer using the plurality ofthird mask portions as a mask to form a plurality of second maskportions; removing the plurality of third mask portions; forming a firstspacer layer over the plurality of second mask portions and the firstmask layer; forming a second spacer layer over the first spacer layer;etching top surfaces of the second spacer layer with a first etchingprocess to expose top surfaces of the first spacer layer; etching theexposed top surfaces of the first spacer layer with a second etchingprocess to expose top surfaces of the first mask layer and to form amask pattern; and patterning the first mask layer and the semiconductordevice layer using the mask pattern as a mask.
 19. The method of claim18 further comprising: forming a material in openings of the patternedsemiconductor device layer.
 20. The method of claim 18, wherein thefirst etching process is selective to the second spacer layer, andwherein the second etching process is selective to the first spacerlayer.